1. Field of the Invention
The present invention relates to a solid type EC (electrochromic) element and a process for producing the same. More particularly, the present invention relates to a solid type EC element in which coloring regions can easily be delimited, coloring regions having a complicated shape can easily be applied, and a phenomenon of blurred color occurring around coloring regions can be prevented.
2. Description of the Related Arts
An EC element is an element which varies a light transmittance by the application of a voltage, and has been utilized in automobile anti-glare mirrors, light modulating windows, display elements and the like. A solid type EC element is an element in which layers making up the EC element are composed of solid materials. FIG. 2 shows a configuration of an automobile EC mirror (inner mirror) having been conventionally put into a practical usage, which utilizes a solid type EC element. A substrate 10 is composed of a transparent glass, and has a lower electrode layer 12 composed of a transparent electrode film such as made of ITO formed on an entire surface of the rear surface thereof. Around a lower side of the lower electrode layer 12, a parting line 14 (groove) is horizontally formed along the lower side, whereby the lower electrode layer 12 is divided into upper and lower regions 12a and 12b, which are not conducted to each other, at the parting line 14 as a boundary.
An EC layer 16 is formed on the lower electrode layer 16 so as to extend over these two regions 12a and 12b of the lower electrode layer 12. The EC layer 16 is composed, for example, of an oxidative coloring layer made, e.g., of a mixture of iridium oxide with tin oxide, a solid electrolyte layer made, e.g., of Ta2O5, and a reductive coloring layer made, e.g., of WO3 laminated in this order. An upper electrode layer 18 comprising a metal-made reflecting film such as made of Al or Cr is formed on the EC layer 16. In the upper electrode layer 18, a region 18b facing to the region 12b of the lower electrode layer 12 is formed so that a part of the region 18b extends outside of the EC layer, and the extending portion of the upper electrode layer 18 is conducted to the region 12a of the lower electrode layer 12. A region 18a of the upper electrode layer 18, facing to the region 12a of the lower electrode layer 12, is formed within the surface of the EC layer 16 as a whole, and is not conducted to the region 12a of the lower electrode layer 12. Clip electrodes 20 and 22 are attached to upper and lower side portions of the substrate 10 as electrode-tapping portions, respectively. The clip electrode 20 is conducted to the region 12a of the lower electrode layer 12, and the clip electrode 22 is conducted to the upper electrode layer 18 via the region 12b of the lower electrode layer 12.
According the configuration described above, when a voltage in a coloring direction is applied between the clip electrodes 20 and 22, the EC layer 16 is colored. In this case, amongst the entire region of the EC layer 16, the region surrounded by the outer edge of the upper electrode layer 18 and the parting line 14 is colored. Subsequently, when a voltage in a reverse direction (voltage in a discoloration direction) is applied between the clip electrodes 20 and 22 or when the clip electrodes 20 and 22 are connected to make a short circuit, the EC layer 16 is discolored.
Referring to FIG. 3, production stages of the conventional automobile EC mirror will be described.
(1) A glass substrate 10 having an ITO film 12 formed on the entire surface thereof as the lower electrode layer is prepared, and a parting line 14 is linearly formed around a lower side of the ITO film 12 parallel to the lower side thereof by etching through a laser beam to divide the ITO film 12 into two regions 12a and 12b. 
(2) The outer edge of the substrate 10 is cut into a mirror form.
(3) A masking member 24 for forming an EC layer is aligned and put on a predetermined position of the substrate 10, and the substrate 10 having being covered with the masking member 24 is accommodated within a vapor deposition apparatus. A material for an oxidative coloring layer, a material for a solid electrolyte layer, and a material for a reductive coloring layer, making up the EC layer, are deposited one after another to form the EC layer 16.
(4) The substrate 10 is taken out from the vapor deposition apparatus, and the masking member 24 for forming an EC layer is removed.
(5) A masking member 26 for forming an upper electrode layer is aligned to and put on a predetermined position of the substrate 10, and the substrate 10 having being covered with the masking member 26 is accommodated within a vapor deposition apparatus. A metal material making up the upper electrode layer is deposited to form the upper electrode layer 10.
(6) The substrate 10 is taken out from the vapor deposition apparatus, and the masking member 26 for forming an upper electrode layer is removed.
(7) The clip electrodes 20 and 22 are attached to upper and lower side portions of the substrate 10. A sealing glass is adhered on the substrate 10 with an adhesive to seal the laminated film to complete the product.
According to the conventional automobile EC mirror, since the coloring region (the region to be colored) 17 is mainly determined by the shape of the upper electrode layer 18, even in the case of products each having a slightly different shape, the masking members 26 for forming an upper electrode layer are required to be separately prepared at the time of forming the upper electrode layer 18 (Stage (5) in FIG. 3). Also, if the shape of the coloring region 17 is complicated, a masking member 26 for forming an upper electrode layer, which corresponds to the complicated shape, should be required.
The conventional automobile EC mirror described above is disadvantageous in the fact that when it is driven in a discoloration direction, blurred color (the situation where the coloring remains blurring) occurs around a portion making up the outer edge of the upper electrode layer 18 amongst the outline of the coloring region 17 (a portion B shown by hatching in FIG. 2). Referring to FIG. 4, the phenomenon of blurred color will be described. FIG. 4A shows a cross sectional view of a portion where the outline of the coloring region 17 is composed of the outer edge of the upper electrode layer 18. In this figure, it is assumed that EC layer 16 is composed of, from the lower layer to the upper layer, a mixed layer 28 of iridium oxide and tin oxide as the oxidative coloring layer, a Ta2O5 layer 30 as the solid electrolyte layer, and a WO3 layer 32 as the reductive coloring layer laminated in this order. In such a configuration, when a voltage is applied taking the upper side as a minus pole and the lower side as a plus pole as shown in FIG. 4B, due to the moisture contained in the Ta2O5 layer 30, H+ ions are captured within the WO3 layer 32 to color the WO3 layer 32 blue. At the same time, OH− ions are captured within the mixed layer 28 of iridium oxide and tin oxide, and the mixed layer 28 of iridium oxide and tin oxide is also colored blue. Subsequently, when a voltage is applied taking the upper side as a plus pole and the lower side as a minus pole as shown in FIG. 4C or when both the upper pole and the lower pole are connected to make a short circuit, H+ ions having been captured within the WO3 layer 32 and OH− ions having been captured within the mixed layer 28 of iridium oxide and tin oxide are returned to the Ta2O5 layer 30, respectively to discolor the WO3 layer 32 and the mixed layer 28 of iridium oxide and tin oxide. However, in such a configuration that the EC layer 16 and the lower electrode layer 12 project outside of the outer edge of the upper electrode layer 18 as shown in FIG. 4A, H+ ions are diffused into a region 32′ (region in which positive and negative electrodes are not facing to each other) projecting outside of the WO3 layer 32, and OH− ions are diffused into a region 28′ (region in which positive and negative electrodes are not facing to each other) projecting outside of the mixed layer 28 of iridium oxide and tin oxide at the time of the coloration as shown in FIG. 4D. Consequently, although the outwardly projecting region 32′ and the outwardly projecting region 28′ are colored, H+ ions and OH− ions cannot be completely returned to the Ta2O5 layer 30 from the outwardly projecting region 32′ and the outwardly projecting region 28′, even when the reverse voltage is applied in order to make a discoloration. As a result, blurred color occurs in these regions 32′ and 28′ [around a portion making up the outer edge of the upper electrode layer 18 amongst the outline of the coloring region 17 (a portion B shown by hatching in FIG. 2)].
The present invention has been made in light of the above situation and is to provide a solid type EC element in which coloring regions having a complicated shape can easily be applied, and a phenomenon of blurred color occurring around coloring regions can be prevented and to provide a process for producing the same.